Power-operated clutch actuator for torque couplings

ABSTRACT

A torque transfer mechanism is provided for controlling the magnitude of a clutch engagement force exerted on a multi-plate clutch assembly that is operably disposed between a first rotary and a second rotary member. The torque transfer mechanism includes a power-operated face gear clutch actuator for generating and applying a clutch engagement force on the clutch assembly.

CROSS REFERENCE

This application claims the benefit of U.S. Provisional Application Ser.No. 60/703,282 filed Jul. 28, 2005, the entire disclosure of which isincorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to power transfer systems forcontrolling the distribution of drive torque between the front and reardrivelines of a four-wheel drive vehicle and/or the left and right wheelof an axle assembly. More particularly, the present invention isdirected to a power transmission device for use in motor vehicledriveline applications having a torque transfer mechanism equipped witha power-operated clutch actuator that is operable for controllingactuation of a multi-plate friction clutch assembly.

BACKGROUND OF THE INVENTION

In view of increased demand for four-wheel drive vehicles, a plethora ofpower transfer systems are currently being developed for incorporationinto vehicular driveline applications for transferring drive torque tothe wheels. In many vehicles, a power transmission device is operablyinstalled between the primary and secondary drivelines. Such powertransmission devices are typically equipped with a torque transfermechanism which is operable for selectively and/or automaticallytransferring drive torque from the primary driveline to the secondarydriveline to establish a four-wheel drive mode of operation.

A modern trend in four-wheel drive motor vehicles is to equip the powertransmission device with a transfer clutch and anelectronically-controlled traction control system. The transfer clutchis operable for automatically directing drive torque to the secondarywheels, without any input or action on the part of the vehicle operator,when traction is lost at the primary wheels for establishing an“on-demand” four-wheel drive mode. Typically, the transfer clutchincludes a multi-plate clutch assembly that is installed between theprimary and secondary drivelines and a clutch actuator for generating aclutch engagement force that is applied to the clutch plate assembly.The clutch actuator typically includes a power-operated device that isactuated in response to electric control signals sent from an electroniccontroller unit (ECU). Variable control of the electric control signalis frequently based on changes in the current operating characteristicsof the vehicle (i.e., vehicle speed, interaxle speed difference,acceleration, steering angle, etc.) as detected by various sensors.Thus, such “on-demand” power transmission devices can utilize adaptivecontrol schemes for automatically controlling torque distribution duringall types of driving and road conditions.

A large number of on-demand power transmission devices have beendeveloped which utilize an electrically-controlled clutch actuator forregulating the amount of drive torque transferred through the clutchassembly to the secondary driveline as a function of the value of theelectrical control signal applied thereto. In some applications, thetransfer clutch employs an electromagnetic clutch as the power-operatedclutch actuator. For example, U.S. Pat. No. 5,407,024 discloses aelectromagnetic coil that is incrementally activated to control movementof a ball-ramp drive assembly for applying a clutch engagement force onthe multi-plate clutch assembly. Likewise, Japanese Laid-open PatentApplication No. 62-18117 discloses a transfer clutch equipped with anelectromagnetic clutch actuator for directly controlling actuation ofthe multi-plate clutch pack assembly.

As an alternative, the transfer clutch may employ an electric motor anda drive assembly as the power-operated clutch actuator. For example,U.S. Pat. No. 5,323,871 discloses an on-demand transfer case having atransfer clutch equipped with an electric motor that controls rotationof a sector plate which, in turn, controls pivotal movement of a leverarm for applying the clutch engagement force to the multi-plate clutchassembly. Moreover, Japanese Laid-open Patent Application No. 63-66927discloses a transfer clutch which uses an electric motor to rotate onecam plate of a ball-ramp operator for engaging the multi-plate clutchassembly. Finally, U.S. Pat. Nos. 4,895,236 and 5,423,235 respectivelydisclose a transfer case equipped with a transfer clutch having anelectric motor driving a reduction gearset for controlling movement of aball screw operator and a ball-ramp operator which, in turn, apply theclutch engagement force to the clutch pack.

While many on-demand clutch control systems similar to those describedabove are currently used in four-wheel drive vehicles, a need exists toadvance the technology and address recognized system limitations. Forexample, the size and weight of the friction clutch components and theelectrical power and actuation time requirements for the clutch actuatorthat are needed to provide the large clutch engagement loads may makesuch a system cost prohibitive in some motor vehicle applications. In aneffort to address these concerns, new technologies are being consideredfor use in power-operated clutch actuator applications.

SUMMARY OF THE INVENTION

Thus, its is an object of the present invention to provide a powertransmission device for use in a motor vehicle having a torque transfermechanism equipped with a power-operated clutch actuator that isoperable to control engagement of a multi-plate clutch assembly.

As a related object, the torque transfer mechanism of the presentinvention is well-suited for use in motor vehicle driveline applicationsto control the transfer of drive torque between a first rotary memberand a second rotary member.

According to one preferred embodiment, a transfer unit is provided foruse in a four-wheel drive motor vehicle having a powertrain and adriveline. The transfer unit includes a first shaft driven by thepowertrain, a second shaft adapted for connection to the driveline and atorque transfer mechanism. The torque transfer mechanism includes afriction clutch assembly operably disposed between the first shaft andthe second shaft and a clutch actuator assembly for generating andapplying a clutch engagement force to the friction clutch assembly. Theclutch actuator assembly includes an electric motor, a geared drive unitand a clutch apply operator. The electric motor drives the geared driveunit which, in turn, controls the direction and amount of rotation of afirst cam member relative to a second cam member associated with theclutch apply operator. The cam members support rollers which rideagainst at least one tapered or ramped cam surface. The contour of thecam surface causes one of the cam members to move axially for causingcorresponding translation of a thrust member. The thrust member appliesthe thrust force generated by the cam members as a clutch engagementforce that is exerted on the friction clutch assembly. A control systemincluding vehicle sensors and a controller are provided to controlactuation of the electric motor.

In accordance with the present invention, the transfer unit isconfigured as a torque coupling for use in adaptively controlling thetransfer of drive torque from the powertrain to the rear drive axle ofan all-wheel drive vehicle. Pursuant to related embodiments, thetransfer unit can be a transfer case for use in adaptively controllingthe transfer of drive torque to the front driveline in an on-demandfour-wheel drive vehicle or between the front and rear drivelines in afull-time four-wheel drive vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages of the present invention willbecome apparent to those skilled in the art from analysis of thefollowing written description, the appended claims, and accompanyingdrawings in which:

FIG. 1 illustrates the drivetrain of an all-wheel drive motor vehicleequipped with a power transmission device of the present invention;

FIG. 2 is a schematic illustration of the power transmission deviceshown in FIG. 1 associated with a drive axle assembly;

FIG. 3 is a partial sectional view of the power transmission devicewhich is equipped with a friction clutch and a clutch actuator assemblyaccording to the present invention;

FIG. 4 is an enlarged partial view of the power transmission devicetaken from FIG. 3;

FIGS. 5 and 6 are detailed views of components of a geared drive unitassociated with the clutch actuator assembly;

FIG. 7 is a partial side view of a face gear of a ball-ramp actuatorcomponent of the clutch actuator assembly according to the presentinvention;

FIG. 8 is a cross-sectional view of an alternative pinion gear of theclutch actuator assembly according to the present invention;

FIGS. 9-12 are schematic illustrations of alternative embodiments forthe power transmission device of the present invention;

FIG. 13 illustrates the drivetrain of a four-wheel drive vehicleequipped with another version of the power transmission device of thepresent invention;

FIGS. 14 and 15 are schematic illustrations of transfer cases adaptedfor use with the drivetrain shown in FIG. 13; and

FIG. 16 is a schematic view of a power transmission device equipped witha torque vectoring distribution mechanism according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a torque transfer mechanism thatcan be adaptively controlled for modulating the torque transferredbetween a first rotary member and a second rotary member. The torquetransfer mechanism finds particular application in power transmissiondevices for use in motor vehicle drivelines such as, for example, anon-demand transfer clutch in a transfer case or an in-line torquecoupling or a biasing clutch associated with a differential unit in atransfer case or a drive axle assembly. Thus, while the presentinvention is hereinafter described in association with particulararrangements for use in specific driveline applications, it will beunderstood that the arrangements shown and described are merely intendedto illustrate embodiments of the present invention.

With particular reference to FIG. 1 of the drawings, a drivetrain 10 foran all-wheel drive vehicle is shown. Drivetrain 10 includes a first orprimary driveline 12, a second or secondary driveline 14 and apowertrain 16 for delivering rotary tractive power (i.e., drive torque)to the drivelines. In the particular arrangement shown, primarydriveline 12 is the front driveline while secondary driveline 14 is therear driveline. Powertrain 16 is shown to include an engine 18 and amulti-speed transmission 20. Front driveline 12 includes a frontdifferential 22 driven by powertrain 16 for transmitting drive torque toa pair of front wheels 24L and 24R through a pair of front axleshafts26L and 26R, respectively. Rear driveline 14 includes a power transferunit 28 driven by powertrain 16 or front differential 22, a propshaft 30driven by power transfer unit 28, a rear axle assembly 32 and a powertransmission device 34 for selectively transferring drive torque frompropshaft 30 to rear axle assembly 32. Rear axle assembly 32 is shown toinclude a rear differential 35, a pair of rear wheels 36L and 36R and apair of rear axleshafts 38L and 38R that interconnect rear differential35 to corresponding rear wheels 36L and 36R.

With continued reference to the drawings, drivetrain 10 is shown tofurther include an electronically-controlled power transfer system forpermitting a vehicle operator to select a locked (“part-time”)four-wheel drive mode, and an adaptive (“on-demand”) four-wheel drivemode. In this regard, power transmission device 34 is equipped with atransfer clutch 50 that can be selectively actuated for transferringdrive torque from propshaft 30 to rear axle assembly 32 for establishingthe part-time and on-demand four-wheel drive modes. The power transfersystem further includes a power-operated clutch actuator 52 foractuating transfer clutch 50, vehicle sensors 54 for detecting certaindynamic and operational characteristics of motor vehicle 10, a modeselect mechanism 56 for permitting the vehicle operator to select one ofthe available drive modes and a controller 58 for controlling actuationof clutch actuator 52 in response to input signals from vehicle sensors54 and mode selector 56.

Power transmission device, hereinafter referred to as torque coupling34, is shown schematically in FIG. 2 to be operably disposed betweenpropshaft 30 and a pinion shaft 60. As seen, pinion shaft 60 includes apinion gear 62 that is meshed with a hypoid ring gear 64 fixed to adifferential case 66 of rear differential 34. Differential 34 isconventional in that pinions 68 driven by case 66 are arranged to driveside gears 70L and 70R which are fixed for rotation with correspondingaxleshafts 38L and 38R. Torque coupling 34 is shown to include transferclutch 50 and clutch actuator 52 arranged to control the transfer ofdrive torque from propshaft 30 to pinion shaft 60 and which togetherdefine the torque transfer mechanism of the present invention.

Referring primarily to FIGS. 3 and 4, the components and function oftorque coupling 34 will be disclosed in detail. As seen, torque coupling34 generally includes a housing 72, an input shaft 74 rotatablysupported in housing 72 via a bearing assembly 76, transfer clutch 50and clutch actuator 52. A yoke 78 is fixed to a first end of input shaft74 to permit connection with propshaft 30. Transfer clutch 50 includes adrum 80 fixed (i.e., splined) for rotation with input shaft 74, a hub 82fixed (i.e., splined) for rotation with pinion shaft 60, and amulti-plate clutch pack 84 comprised of alternating inner and outerclutch plates that are disposed between drum 80 and hub 82. As shown, abearing assembly 86 rotatably supports a second end of input shaft 74 ona piloted end portion of pinion shaft 60, which, in turn, is rotatablysupported in housing 72 via a pair of bearing assemblies 88.

Clutch actuator 52 is generally shown to include an electric motor 90, ageared drive unit 92 and a clutch apply operator 94. Electric motor 90is secured to housing 72 and includes a rotary output shaft 96. Geareddrive unit 92 is driven by motor output shaft 96 and functions tocontrol relative movement between components of clutch apply operator 94for controlling the magnitude of a clutch engagement force applied toclutch pack 84 of transfer clutch 50. In addition, geared drive unit 92includes first and second gearsets which provide a desired speedreduction between motor shaft 96 and a rotary component of clutch applyoperator 94. Specifically, the first gearset includes a first gear 98driven by motor shaft 96 that is meshed with second gear 102. Pursuantto one preferred embodiment, first gear 98 is a worm that is formedintegrally on or fixed to motor shaft 96 while second gear 102 is a wormgear. Likewise, the second gearset includes a third gear 104 that ismeshed with a fourth gear 106 associated with clutch apply operator 94.Preferably, third gear 104 is a pinion gear while fourth gear 106 is ahelical face gear. To permit the first gearset to drive the secondgearset, worm gear 102 is fixed to pinion gear 104 to define a compoundgear 100 that is rotatable about an axis B. It is contemplated thatalternative planetary gear arrangements could be used in geared driveunit 92 instead of the worm gearing.

Clutch apply operator 94 is best shown in FIG. 4 to include a first camplate 130 non-rotatably fixed via a spline connection 132 to housing 72,a second cam plate 134 that is rotatable about pinion shaft 60 and theaxis A, and balls 138. As seen, face gear 106 of geared drive unit 92 isfixed to second cam plate 134. In addition, a ball 138 is disposed ineach of a plurality of aligned cam grooves 140 and 142 formed incorresponding facing surfaces of first and second cam plates 130 and134, respectively. Preferably, three equally-spaced sets of such facingcam grooves 140 and 142 are formed in cam plates 130 and 134,respectively. Grooves 140 and 142 are formed as cam surfaces that areramped, tapered or otherwise contoured in a circumferential direction.Balls 138 roll against cam surfaces 140 and 142 so as to cause axialmovement of second cam plate 134 relative to first cam plate 130 alongthe axis A.

A first thrust bearing assembly 144 is disposed between second cam plate130 and an actuator plate 146 of clutch pack 84. As seen, hub 82includes a reaction ring 147 with clutch pack 84 located betweenreaction ring 147 and actuator plate 146. A return spring 148 and asecond thrust bearing assembly 149 are disposed between hub 82 andactuator plate 146. As an alternative to the arrangement shown, one ofcam surfaces 140 and 142 can be non-tapered such that the rampingprofile is configured entirely within the other of the cam surfaces.Also, balls 138 are shown be spherical but are contemplated to permituse of cylindrical rollers disposed in correspondingly shaped camgrooves or surfaces.

Second cam plate 134 is axially moveable relative to clutch pack 84between a first or “released” position and a second or “locked”position. With second cam plate 134 in its released position, a minimumclutch engagement force is exerted by actuator plate 146 on clutch pack84 such that virtually no drive torque is transferred from input shaft74 through clutch pack 84 to pinion shaft 60. In this manner, atwo-wheel drive mode is established. Return spring 148 is provided tonormally bias second cam plate 132 toward its released position. Incontrast, location of second cam plate 134 in its locked position causesa maximum clutch engagement force to be applied by actuator plate 146 toclutch pack 84 such that pinion shaft 60 is, in effect, coupled forcommon rotation with input shaft 74. In this manner, the locked orpart-time four-wheel drive mode is established. Therefore, accuratebidirectional control of the axial position of second cam plate 134between its released and locked positions permits adaptive regulation ofthe amount of drive torque transferred from input shaft 74 to pinionshaft 60, thereby establishing the on-demand four-wheel drive mode.

The tapered contour of cam surfaces 140 and 142 is selected to controlthe axial translation of second cam plate 134 relative to clutch pack 84from its released position to its locked position in response to worm 98being driven by motor 90 in a first rotary direction. Such rotation ofworm 98 in a first direction induces rotation of compound gear 100 aboutaxis B, which causes face gear 106 to rotate second cam plate 134 aboutaxis A in a first direction. As a result, corresponding relativerotation between cam plates 130 and 134 occurs such that balls 138 rideagainst contoured cam surfaces 140 and 142. However, since first camplate 130 is restrained against axial and rotational movement, suchrotation of second cam plate 134 causes concurrent axial movement ofsecond cam plate 134 toward its locked position for increasing theclutch engagement force on clutch pack 84.

Referring now primarily to FIGS. 3, 5 and 6, clutch actuator 52 can bepositioned to account for in-vehicle packaging requirements. Forexample, as illustrated in FIGS. 3 and 5, the rotary axis “C” of shaft96 of electric motor 90 is aligned parallel to axis A extending alongpower transmission device 34 and is also perpendicular to axis B. Asillustrated in FIG. 6, electric motor 90 is perpendicular to axis A,extending from power transmission device 34. Further, electric motor 90can be angularly positioned at an angle a relative to a horizontal axisC of power transmission device 34 to further accommodate in-vehiclepackaging requirements.

Referring to FIGS. 7 and 8, the interface between the teeth of piniongear 104 and face gear 106 will be described in further detail. In oneembodiment (FIG. 7), face gear 106 includes a ramp or helix angle β,whereby its helical teeth steadily increase in elevation relative to aplane D. Ramp angle β corresponds to the ramp or taper angle ofcontoured cam surfaces 140 and 142, thereby compensating for axialmovement of second cam plate 134 away from pinion gear 104 along axis A.In this manner, pinion gear 104 and face gear 106 remain in meshedengagement as clutch apply operator 94 acts on transfer clutch 50. Inanother embodiment (FIG. 8), pinion gear 104′ includes an oblongcross-section, whereby its teeth are at varying distances fromrotational axis B. The oblong cross-section compensates for movement ofsecond cam plate 134 away from pinion gear 104′ along axis A. In thismanner, pinion gear 104′ and face gear 106 remain in meshed engagementas clutch apply operator 94 acts on transfer clutch 50. It isanticipated that ramp angle β and the oblong cross-section can beimplemented individually or in concert to maintain meshed engagement ofpinion gear 104′ and face gear 106 as clutch apply operator 94 activatestransfer clutch 50.

In operation, when mode selector 56 indicates selection of the two-wheeldrive mode, controller 58 signals electric motor 90 to rotate motorshaft 96 in the second direction for moving second cam plate 134 untilit is located in its released position, thereby releasing clutch pack84. As noted, return spring 148 assists in returning second cam plate134 to its released position. If mode selector 56 thereafter indicatesselection of the part-time four-wheel drive mode, electric motor 90 issignaled by controller 58 to rotate motor 96 in the first direction forinducing axial translation of second cam plate 134 until it is locatedin its locked position. As noted, such axial movement of second camplate 134 to its locked position acts to fully engage clutch pack 84,thereby coupling pinion shaft 60 to input shaft 74.

When mode selector 56 indicates selection of the on-demand four-wheeldrive mode, controller 58 energizes electric motor 90 to rotate motor 96until second cam plate 134 is axially located in a ready or “stand-by”position. This position may be its released position or, in thealternative, an intermediate position. In either case, a predeterminedminimum amount of drive torque is delivered to pinion shaft 60 throughclutch pack 84 in this stand-by condition. Thereafter, controller 58determines when and how much drive torque needs to be transferred topinion shaft 60 based on current tractive conditions and/or operatingcharacteristics of the motor vehicle, as detected by sensors 54. As willbe appreciated, any control schemes known in the art can be used withthe present invention for adaptively controlling actuation of transferclutch 50 in a driveline application. The arrangement described forclutch actuator 52 is an improvement over the prior art in that thetorque amplification provided by geared drive unit 92 permits use of asmall low-power electric motor and yet provides extremely quick responseand precise control. Other advantages are realized in the reduced numberof components and packaging flexibility.

To illustrate an alternative power transmission device to which thepresent invention is applicable, FIG. 9 schematically depicts afront-wheel based four-wheel drivetrain layout 10′ for a motor vehicle.In particular, engine 18 drives multi-speed transmission 20 having anintegrated front differential unit 22 for driving front wheels 24L and24R via axleshafts 26L and 26R. A power transfer unit 190 is also drivenby powertrain 16 for delivering drive torque to the input member of atorque transfer mechanism, hereinafter referred to as torque coupling192, that is operable for selectively transferring drive torque topropshaft 30. Accordingly, when sensors indicate the occurrence of afront wheel slip condition, controller 58 adaptively controls actuationof torque coupling 192 such that drive torque is delivered “on-demand”to rear driveline 14 for driving rear wheels 36L and 36R. It iscontemplated that torque transfer coupling 192 would include amulti-plate clutch assembly 194 and a clutch actuator 196 that aregenerally similar in structure and function to multi-plate transferclutch 50 and clutch actuator 52 previously described herein.

Referring now to FIG. 10, power transfer unit 190 is now schematicallyillustrated in association with an on-demand all-wheel drive systembased on a front-wheel drive vehicle similar to that shown in FIG. 9. Inparticular, an output shaft 202 of transmission 20 is shown to drive anoutput gear 204 which, in turn, drives an input gear 206 fixed to acarrier 208 associated with front differential unit 22. To provide drivetorque to front wheels 24L and 24R, front differential 22 furtherincludes a pair of side gears 210L and 210R that are connected to thefront wheels via corresponding axleshafts 26L and 26R. Differential unit22 also includes pinions 212 that are rotatably supported on pinionshafts fixed to carrier 208 and which are meshed with both side gears210L and 210R. A transfer shaft 214 is provided to transfer drive torquefrom carrier 208 to torque coupling 192.

Power transfer unit 190 includes a right-angled drive mechanism having aring gear 220 fixed for rotation with a drum 222 of clutch assembly 194and which is meshed with a pinion gear 224 fixed for rotation withpropshaft 30. As seen, a clutch hub 216 of clutch assembly 194 is drivenby transfer shaft 214 while a clutch pack 228 is disposed between hub216 and drum 222. Clutch actuator assembly 196 is operable forcontrolling engagement of clutch assembly 194. Clutch actuator assembly196 is intended to be similar to motor-driven clutch actuator assembly52 previously described in that an electric motor is supplied withelectric current for controlling relative rotation of a geared driveunit which, in turn, controls translational movement of a cam plateoperator for controlling engagement of clutch pack 228.

In operation, drive torque is transferred from the primary (i.e., front)driveline to the secondary (i.e., rear) driveline in accordance with theparticular mode selected by the vehicle operator via mode selector 56.For example, if the on-demand four-wheel drive mode is selected,controller 58 modulates actuation of clutch actuator assembly 196 inresponse to the vehicle operating conditions detected by sensors 54 byvarying the value of the electric control signal sent to the electricmotor. In this manner, the level of clutch engagement and the amount ofdrive torque that is transferred through clutch pack 228 to reardriveline 14 through power transfer unit 190 is adaptively controlled.Selection of the part-time four-wheel drive mode results in fullengagement of clutch assembly 194 for rigidly coupling the frontdriveline to the rear driveline. In some applications, mode selector 56may be eliminated such that only the on-demand four-wheel drive mode isavailable so as to continuously provide adaptive traction controlwithout input from the vehicle operator.

FIG. 11 illustrates a modified version of FIG. 10 wherein an on-demandfour-wheel drive system is shown based on a rear-wheel drive motorvehicle that is arranged to normally deliver drive torque to reardriveline 14 while selectively transmitting drive torque to front wheels24L and 24R through torque coupling 192. In this arrangement, drivetorque is transmitted directly from transmission output shaft 202 totransfer unit 190 via a drive shaft 230 interconnecting input gear 206to ring gear 220. To provide drive torque to the front wheels, torquecoupling 192 is shown operably disposed between drive shaft 230 andtransfer shaft 214. In particular, clutch assembly 194 is arranged suchthat drum 222 is driven with ring gear 220 by drive shaft 230. As such,actuation of clutch actuator 196 functions to transfer torque from drum222 through clutch pack 228 to hub 216 which, in turn, drives carrier208 of front differential unit 22 via transfer shaft 214. Again, thevehicle could be equipped with mode selector 56 to permit selection bythe vehicle operator of either the adaptively controlled on-demandfour-wheel drive mode or the locked part-time four-wheel drive mode. Invehicles without mode selector 56, the on-demand four-wheel drive modeis the only drive mode available and provides continuous adaptivetraction control without input from the vehicle operator.

In addition to the on-demand 4WD systems shown previously, the powertransmission technology of the present invention can likewise be used infull-time 4WD systems to adaptively bias the torque distributiontransmitted by a center or “interaxle” differential unit to the frontand rear drivelines. For example, FIG. 12 schematically illustrates afull-time four-wheel drive system which is generally similar to theon-demand four-wheel drive system shown in FIG. 10 with the exceptionthat power transfer unit 190 now includes an interaxle differential unit240 that is operably installed between carrier 208 of front differentialunit 22 and transfer shaft 214. In particular, output gear 206 is fixedfor rotation with a carrier 242 of interaxle differential 240 from whichpinion gears 244 are rotatably supported. A first side gear 246 ismeshed with pinion gears 244 and is fixed for rotation with drive shaft230 so as to be drivingly interconnected to rear driveline 14 throughtransfer gearset 220 and 224. Likewise, a second side gear 248 is meshedwith pinion gears 244 and is fixed for rotation with carrier 208 offront differential unit 22 so as to be drivingly interconnected to thefront driveline. Torque coupling 192 is now shown to be operablydisposed between side gears 246 and 248. As such, torque coupling 192 isoperably arranged between the driven outputs of interaxle differential240 for providing a torque biasing and slip limiting function. Torquecoupling 192 is shown to again include multi-plate clutch assembly 194and clutch actuator assembly 196. Clutch assembly 194 is operablyarranged between transfer shaft 214 and driveshaft 230. In operation,when sensor 54 detects a vehicle operating condition, such as excessiveinteraxle slip, controller 58 adaptively controls activation of theelectric motor associated with clutch actuator assembly 196 forcontrolling engagement of clutch assembly 194 and thus the torquebiasing between the front and rear drivelines.

Referring now to FIG. 13, a schematic layout of a drivetrain 10A for afour-wheel drive vehicle having powertrain 16 delivering drive torque toa power transfer unit, hereinafter referred to as transfer case 290.Transfer case 290 includes a rear output shaft 302, a front output shaft304 and a torque coupling 292 therebetween. Torque coupling 292generally includes a multi-plate transfer clutch 294 and apower-operated clutch actuator 296. As seen, a rear propshaft 306couples rear output shaft 302 to rear differential 34 while a frontpropshaft 308 couples front output shaft 304 to front differential 22.Power-operated clutch actuator 296 is again schematically shown toprovide adaptive control over engagement of multi-plate clutch assembly294 incorporated into transfer case 290.

Referring now to FIG. 14, a full-time 4WD system is shown to includetransfer case 290 equipped with an interaxle differential 310 between aninput shaft 312 and output shafts 302 and 304. Differential 310 includesan input defined as a planet carrier 314, a first output defined as afirst sun gear 316, a second output defined as a second sun gear 318,and a gearset for permitting speed differentiation between first andsecond sun gears 316 and 318. The gearset includes meshed pairs of firstplanet gears 320 and second planet gears 322 which are rotatablysupported by carrier 314. First planet gears 320 are shown to mesh withfirst sun gear 316 while second planet gears 322 are meshed with secondsun gear 318. First sun gear 316 is fixed for rotation with rear outputshaft 302 so as to transmit drive torque to the rear driveline. Totransmit drive torque to the front driveline, second sun gear 318 iscoupled to a transfer assembly 324 which includes a first sprocket 326rotatably supported on rear output shaft 302, a second sprocket 328fixed to front output shaft 304, and a power chain 330.

As noted, transfer case 290 includes clutch assembly 294 and clutchactuator 296. Clutch assembly 294 has a drum 332 fixed to sprocket 326for rotation with front output shaft 304, a hub 334 fixed for rotationwith rear output shaft 302 and a multi-plate clutch pack 336therebetween. Again, clutch actuator 296 is schematically shown butintended to be substantially similar in structure and function to thatdisclosed in association with clutch actuator 52 shown in FIGS. 3 and 4.FIG. 15 is merely a modified version of transfer case 290 which isconstructed without center differential 310 to provide an on-demandfour-wheel drive system.

Referring now to FIG. 16, a drive axle assembly 400 is schematicallyshown to include a pair of torque couplings operably installed betweendriven propshaft 30 and rear axleshafts 38L and 38R. Propshaft 30 drivesa right-angle gearset including pinion 402 and ring gear 404 which, inturn, drives a transfer shaft 406. A first torque coupling 408L is showndisposed between transfer shaft 406 and left axleshaft 38L while asecond torque coupling 408R is disposed between transfer shaft 406 andright axleshaft 38R. Each of the torque couplings can be independentlycontrolled via activation of its corresponding clutch actuator assembly410L, 410R to adaptively control engagement of corresponding multi-plateclutch assemblies 412L and 412R for controlling side-to-side torquedelivery. In a preferred application, axle assembly 400 can be used inassociation with the secondary driveline in four-wheel drive motorvehicles.

A number of preferred embodiments have been disclosed to provide thoseskilled in the art an understanding of the best mode currentlycontemplated for the operation and construction of the presentinvention. The invention being thus described, it will be obvious thatvarious modifications can be made without departing from the true spiritand scope of the invention, and all such modifications as would beconsidered by those skilled in the art are intended to be includedwithin the scope of the following claims.

1. A power transmission device comprising: a rotary input member adaptedto receive drive torque from a power source; a rotary output memberadapted to provide drive torque to an output device; a torque transfermechanism operable for transferring drive torque from said input memberto said output member, said torque transfer mechanism including a clutchassembly operably disposed between said input member and said outputmember and a clutch actuator assembly for applying a clutch engagementforce to said clutch assembly, said clutch actuator assembly includingan electric motor driving a geared drive unit for controlling saidclutch engagement force applied to said clutch assembly by a clutchapply operator, said geared drive unit includes a pinion gear driven bysaid electric motor and a face gear in meshed engagement with saidpinion gear, said clutch apply operator including a first cam platefixed against rotation, a second cam plate fixed for rotation with saidface gear and rollers engaging a cam surface provided between said firstand second cam plates, wherein said face gear includes a ramp angleadapted to accommodate axial movement of said second cam plate relativeto said pinion gear; and a control system for actuating said electricmotor so as to control the direction and amount of rotation of said facegear which, in turn, controls the direction and amount of translationalmovement of said second cam plate relative to said clutch assembly. 2.The power transmission device of claim 1 wherein said second cam plateincludes a ring segment having a face surface with helical gear teethformed thereon to define said face gear, and wherein said face surfaceincludes said ramp angle.
 3. The power transmission device of claim 1wherein said pinion gear includes an oblong cross-section sized toaccommodate axial movement of said second cam plate relative to saidpinion gear.
 4. The power transmission device of claim 1 wherein saidgeared drive unit further includes a worm gear driving said pinion gearand which is meshed with a worm fixed to a motor shaft driven by saidelectric motor.
 5. The power transmission device of claim 4 wherein arotational axis of said motor shaft is at an angle relative to arotational axis of said pinion gear.
 6. The power transmission device ofclaim 4 wherein a rotational axis of said motor shaft is a perpendicularto a rotational axis of said pinion gear.
 7. The power transmissiondevice of claim 1 wherein said control system includes a controller forreceiving input signals from a sensor and generating electric controlsignals based on said input signals which are supplied to said electricmotor for controlling the direction and amount of rotary movement ofsaid face gear.
 8. The power transmission device of claim 1 wherein saidinput member provides drive torque to a first driveline of a motorvehicle, wherein said output member is coupled to a second driveline ofthe motor vehicle, and wherein said torque transfer mechanism isoperable to transfer drive torque from said input member to said outputmember.
 9. The power transmission device of claim 8 defining a transfercase wherein said input member is a first shaft driving the firstdriveline and said output member is a second shaft coupled to the seconddriveline, wherein location of said second cam plate in a first positionreleases engagement of said clutch assembly so as to define a two-wheeldrive mode and location of said second cam plate in a second positionfully engages said clutch assembly so as to define a part-timefour-wheel drive mode, and wherein said control system is operable tocontrol activation of said electric motor for varying the position ofsaid second cam plate between its first and second positions tocontrollably vary the drive torque transferred from said first shaft tosaid second shaft so as to define an on-demand four-wheel drive mode.10. The power transmission device of claim 8 defining a power take-offunit wherein said input member provides drive torque to a firstdifferential associated with the first driveline, and wherein saidoutput member is coupled to a second differential associated with thesecond driveline.
 11. The power transmission device of claim 1 whereinsaid input member is a propshaft driven by a drivetrain of a motorvehicle and said output member is a pinion shaft driving a differentialassociated with an axle assembly of the motor vehicle, and wherein saidclutch assembly is disposed between said propshaft and said pinion shaftsuch that actuation of said clutch actuator assembly is operable totransfer drive torque from said propshaft to said pinion shaft.
 12. Thepower transmission device of claim 1 wherein said input member includesa first differential supplying drive torque to a pair of first wheels ina motor vehicle and a transfer shaft driven by said differential, saidoutput member includes a propshaft coupled to a second differentialinterconnecting a pair of second wheels in the motor vehicle, andwherein said clutch assembly is disposed between said transfer shaft andsaid propshaft.
 13. The power transmission device of claim 1 whereinsaid input member includes a first shaft supplying drive torque to asecond shaft which is coupled to a first differential for driving a pairof first wheels in a motor vehicle, said output member is a third shaftdriving a second differential interconnecting a pair of second wheels ofthe motor vehicle, and wherein said clutch assembly is operably disposedbetween said first and third shafts.
 14. The power transmission deviceof claim 1 further including an interaxle differential driven by saidinput member and having a first output driving a first driveline in amotor vehicle and a second output driving a second driveline in themotor vehicle, and wherein said clutch assembly is operably disposedbetween said first and second outputs of said interaxle differential.15. A torque transfer mechanism for transferring drive torque from arotary input member to a rotary output member, comprising: a frictionclutch assembly having a drum fixed for rotation with one of the inputmember and the output member, a hub fixed for rotation with the other ofthe input member and the output member, a clutch pack operably disposedbetween said drum and said hub, and an actuator plate moveable between afirst position whereat a minimum clutch engagement force is exerted onsaid clutch pack and a second position whereat a maximum clutchengagement force is exerted on said clutch pack; a clutch actuatorassembly for moving said actuator plate between its first and secondpositions and including an electric motor driving a geared drive unitfor controlling movement of a clutch apply operator, said geared driveunit includes a pinion gear driven by said electric motor and a facegear in meshed engagement with said pinion gear so as to cause said facegear to rotate in response to driven rotation of said pinion gear, saidclutch apply operator including a first cam plate, a second cam platefixed for rotation with said face gear and rollers engaging a camsurface between said first and second cam plates, wherein said face gearincludes a ramp angle adapted to compensate for axial movement of saidsecond cam plate relative to said pinion gear; and a control system foractuating said electric motor so as to control rotary movement of saidface gear relative to said pinion gear between a first position and asecond position, said first cam plate being located in a first axialposition when said face gear is in its first position so as to causesaid actuator plate to be located in its first position, and said firstcam plate is located in a second axial position when said first facegear is rotated to its second position so as to cause said actuatorplate to move to its second position.
 16. The torque transfer mechanismof claim 15 wherein said second cam plate includes a hub segmentrotatably supported about a rotary axis and a ring segment having gearteeth of said face gear formed on a face surface, and wherein said facesurface includes said ramp angle.
 17. The torque transfer mechanism ofclaim 15 wherein said pinion gear includes an oblong cross-section tocompensate for movement of said second cam plate relative to said piniongear, and wherein teeth of said pinion gear are at varying distancesfrom a rotational axis of said pinion gear.
 18. The torque transfermechanism of claim 15 further comprising a worm gear driving said piniongear and which is meshed with a worm that is fixed to a shaft driven bysaid electric motor.
 19. The torque transfer mechanism of claim 18wherein a rotational axis of said shaft is at an angle relative to arotational axis of said pinion gear.
 20. The torque transfer mechanismof claim 18 wherein a rotational axis of said shaft is a perpendicularto a rotational axis of said pinion gear.
 21. The torque transfermechanism of claim 15 defining a transfer case wherein said input memberis a first shaft driving a first driveline and the output member is asecond shaft coupled to a second driveline, wherein location of saidsecond cam plate in a first position releases engagement of said clutchassembly so as to define a two-wheel drive mode and location of saidsecond cam plate in a second position fully engages said clutch assemblyso as to define a part-time four-wheel drive mode, and wherein saidcontrol system is operable to control activation of said electric motorfor varying the position of said second cam plate between said first andsecond positions to controllably vary the drive torque transferred fromsaid first shaft to said second shaft so as to define an on-demandfour-wheel drive mode.
 22. The torque transfer mechanism of claim 21wherein said control system includes a controller for receiving inputsignals from a sensor and generating electric control signals based onsaid input signals which are supplied to said electric motor forcontrolling the direction and amount of rotary movement of said piniongear.
 23. The torque transfer mechanism of claim 15 defining a powertake-off unit wherein the input member provides drive torque to a firstdifferential associated with a first driveline, and wherein the outputmember is coupled to a second differential associated with a seconddriveline.
 24. The torque transfer mechanism of claim 15 wherein theinput member is a propshaft driven by a drivetrain of a motor vehicleand the output member is a pinion shaft driving a differentialassociated with an axle assembly of the motor vehicle, and wherein saidclutch assembly is disposed between said propshaft and said pinion shaftsuch that actuation of said clutch actuator assembly is operable totransfer drive torque from said propshaft to said pinion shaft.
 25. Thetorque transfer mechanism of claim 15 wherein the input member includesa first differential supplying drive torque to a pair of first wheels ina motor vehicle, and a transfer shaft driven by said first differential,the output member includes a propshaft coupled to a second differentialinterconnecting a pair of second wheels in the motor vehicle, andwherein said clutch assembly is disposed between said transfer shaft andsaid propshaft.
 26. The power transmission device of claim 15 whereinthe input member includes a first shaft supplying drive torque to asecond shaft which is coupled to a first differential for driving a pairof first wheels in a motor vehicle and the output member is a thirdshaft driving a second differential interconnecting a pair of secondwheels of the motor vehicle, and wherein said clutch assembly isoperably disposed between said first and third shafts.
 27. A powertransmission device, comprising: a rotary input shaft adapted to receivedrive torque from a power source; a rotary output shaft adapted toprovide drive torque to an output device; a friction clutch operablydisposed between said rotary input and output shafts; a clutch actuatorfor generating and applying a clutch engagement force to said frictionclutch, said clutch actuator including an electric motor, a geared driveunit driven by said electric motor and a clutch operator actuated bysaid geared drive unit, said geared drive unit including a worm drivenby said electric motor, a compound gear having a worm gear meshed withsaid worm and a pinion gear, and a face gear meshed with said piniongear, said clutch operator including a first cam member, a second cammember fixed for rotation with said face gear and adapted to moveaxially in response to rotation relative to said first cam member forcontrollably varying the magnitude of said clutch engagement forceapplied to said friction clutch; and a control system for actuating saidelectric motor for causing said geared drive unit to control thedirection and amount of rotation of said face gear.